The invention relates to an electronic device, and more particularly, to an image sensor device.
Solid state image sensors are necessary components in many optoelectronic devices, including digital cameras, cellular phones, and others. Conventional solid-state image sensors for color analog or digital video cameras comprise typically charge-coupled devices (CCD) or complementary metal oxide semiconductor (CMOS) photodiode array structures which comprise a spectrally photosensitive layer below one or more layers patterned in an array of color filters and above which resides a surface-layer array of microlens elements. The elementary unit of the image sensor is defined as a pixel. The basic technology used to form the CMOS image sensor is common to both sensor types.
The CMOS image sensor comprises a photo detector detecting light and a logic circuit converting the detected light into an electric signal representing data regarding the detected light. The fill factor, sometimes referred to as the aperture efficiency, is the ratio of the size of the light-sensitive area to the size of the total pixel. Although efforts have been made to increase the fill factor of an image sensor and thereby increase sensor sensitivity, further increases in the fill factor are limited because the associated logic circuitry cannot be completely removed. To increase the sensitivity of the light, microlens formation technology has been used to converge and focus incident light onto a photo detector by changing the path of the light to the lens of the photo detector. For the image sensor to detect and provide a color image, it typically must employ both a photo detector receiving the light and generating and accumulating charge carriers and a color filter array (CFA), i.e., a plurality of color filter units sequentially arranged above the photo detector. The CFA typically uses one of two alternative three-color primary configurations, either red R, green G and blue B (RGB) configuration or one of yellow Y, magenta M and cyan C (CMY). A plurality of microlenses are positioned above the color filter array to increase the photo-sensitivity of the image sensor.
FIG. 1 is a cross section illustrating a typical image sensor device. In FIG. 1, a typical image sensor device 100 is illustrated in cross section, including a semiconductor substrate 101 having an array of photodiodes 120 therein. Each photodiode 120 has, for example, an n-type region 124 in a p-type region 122. Each photodiode 120 is separated from others by an array of isolation structures 110, such as shallow trench isolation (STI). Thus, an array of pixels is obtained. The pixels convert incoming light 160 from a light/image source to electrical signals via the photodiodes 124. The substrate 101 is covered by a series of dielectric layers 130, such as interlevel dielectric (ILD) layers and intermetal dielectric (IMD) layers. A color filter layer 140 overlying the substrate 101 includes red regions 140a, green regions 140b and blue regions 140c. In this image sensor device, however, electrons in a pixel are likely to pass to neighboring pixels through the substrate thereunder. This phenomenon is referred as electric crosstalk. Specifically, as pixel size is reduced, electric crosstalk increases. In addition, conventional image sensor cannot provide uniform sensitivity to the three major colors.